1. Field of the Invention
The present invention relates to the design of an optical network unit (ONU). More specifically, the present invention relates to the design of an in-wall ONU powered via Power-over-Ethernet (PoE) which could be supplied by Customer Premises Equipment (CPE) such as a home network gateway or an enterprise router.
2. Related Art
In order to keep pace with increasing Internet traffic, network operators have widely deployed optical fibers and optical transmission equipment, substantially increasing the capacity of backbone networks. A corresponding increase in access network capacity, however, has not matched this increase in backbone network capacity. Even with broadband solutions, such as digital subscriber line (DSL) and cable modem (CM), the limited bandwidth offered by current access networks still presents a severe bottleneck in delivering large bandwidth to end users.
Among different competing technologies, passive optical networks (PONs) are one of the best candidates for next-generation access networks. With the large bandwidth of optical fibers, PONs can accommodate broadband voice, data, and video traffic simultaneously. Such integrated service is difficult to provide with DSL or CM technology. Furthermore, PONs can be built with existing protocols, such as Ethernet and ATM, which facilitate interoperability between PONs and other network equipment.
Typically, PONs are used in the “first mile” of the network, which provides connectivity between the service provider's central offices and the premises of the customers. The “first mile” is generally a logical point-to-multipoint network, where a central office serves a number of customers. For example, a PON can adopt a tree topology, wherein one trunk fiber couples the central office to a passive optical splitter/combiner. Through a number of branch fibers, the passive optical splitter/combiner divides and distributes downstream optical signals to customers and combines upstream optical signals from customers (see FIG. 1). Note that other topologies, such as ring and mesh topologies, are also possible.
Transmissions within a PON are typically performed between an optical line terminal (OLT) and optical network units (ONUs). The OLT generally resides in the central office and couples the optical access network to a metro backbone, which can be an external network belonging to, for example, an Internet service provider (ISP) or a local exchange carrier. The ONU can reside in the residence of the customer and couples to the customer's own home network through a customer-premises equipment (CPE). Examples of a CPE include a home network gateway, a Gigabit Ethernet (GbE) switch, or an enterprise router.
In the example of an Ethernet PON (EPON), communications can include downstream traffic and upstream traffic. In the following description, “downstream” refers to the direction from an OLT to one or more ONU, and “upstream” refers to the direction from an ONU to the OLT. In the downstream direction, because of the broadcast nature of the 1xN passive optical coupler, data packets are broadcast by the OLT to all ONUs and are selectively extracted by their destination ONUs. Moreover, each ONU is assigned one or more Logical Link Identifiers (LLIDs), and a data packet transmitted by the OLT typically specifies an LLID of the destination ONU. In the upstream direction, the ONUs need to share channel capacity and resources, because there is only one link coupling the passive optical coupler to the OLT.
A conventional ONU requires its own power supply in order to function. Such requirement is inconvenient to carriers who set up ONUs on customers' premises because it limits positions of the ONUs to places that are close to power outlets. Power outlets may be scarce within a customer's home or office, or may be far away from the point where the optical fiber of the access network, e.g., the EPON, enters the customer's premise. A single strand optical fiber that leaves the EPON to connect to the ONU, although protected by a fiber jacket, is still prone to environmental and mechanical damage, such as contamination of the fiber interface and pulling or acute bending of the fiber.